Methods for controlled laser-induced growth of glass bumps on glass articles

ABSTRACT

A method for controlling formation of glass bumps in a glass article with laser-irradiation without the use of a growth-limiting structure. Standard deviation of height between the glass bumps on the article is less than 1 micron by controlling the laser radiation dose provided on the glass article.

BACKGROUND

The present disclosure relates to methods for controlling formation ofglass bumps on glass articles, the glass bumps having a height within astandard deviation.

SUMMARY

The present inventors have recognized that conventional glass bumpgrowth methodologies can be enhanced by utilizing a laser controlscheme. By utilizing the presently disclosed bump height controlmethods, the standard deviation of height between a plurality of glassbumps formed on a glass article is significantly reduced. Although theconcepts of the present disclosure are described herein with primaryreference to VIG glass products, such as, e.g., VIG windows, theconcepts disclosed herein will enjoy broad applicability to anyapplication where glass bumps of uniform height are required on a glassarticle. It is contemplated that the concepts disclosed herein willenjoy applicability to any laser-induced glass bump growth processwithout limitation to the particular laser growth system disclosedherein.

According to one embodiment of the present disclosure, a method offorming a glass article comprising a surface and a plurality of glassbumps is disclosed. The glass bumps are formed in the glass article bylaser radiation. Each glass bump has a terminal point at a distance fromthe glass article surface. The standard deviation of distance betweenthe glass article surface and the terminal points of the plurality ofglass bumps is less than about 1 micron. According to the method, theglass article is irradiated with laser radiation at a plurality oflocalities. A back flash of light is detected from the laser irradiatedlocalities on the glass article by a photodetector that generates anelectronic signal. The laser irradiation dose at the plurality oflocalities is controlled using the electronic signal to induce growth ofthe glass bumps at the plurality of localities on the glass article.

According to another embodiment of the present disclosure, a method offorming a glass pane comprising a surface and a plurality ofhemispherical glass bumps is disclosed. The glass bumps are grown on theglass pane surface by laser irradiation. Each glass bump has a heightspaced apart from the glass pane surface. The standard deviation ofheight between the plurality of glass bumps is less than 1 micron.According to the method, the glass pane is irradiated with laserradiation to induce growth of one of the glass bumps at one of aplurality of localities on the glass pane. At a time increment afterirradiating one locality with the laser irradiation dose, a back flashof light is detected from that laser irradiated locality with aphotodetector. The laser radiation dose is terminated at the locality ata time after the photo detector detects the back flash of light.

According to yet another embodiment of the present disclosure, a glasspane including a plurality of glass bumps formed on a surface of theglass pane is disclosed. Each glass bump comprises a lower region and anupper region connected by an inflection region. The lower regioncomprises a diameter D1 defined by concavely rounded sides. The lowerregion projects from the surface of the glass pane. The diameter D1 isthe glass bump maximum diameter. The concavely rounded sides have aradius of curvature R1 and join with the glass pane surface. The upperregion of the glass bump comprises a transition portion and a topportion. The transition portion comprises a diameter D2 defined byconvexly rounded sides, diameter D2 is less than diameter D1. Theconvexly rounded sides have a radius of curvature R2. The top portioncomprises a diameter D3 defined by a convexly rounded top surfacejoining with convexly rounded sides converging from the transitionportion. The convexly rounded top surface has a radius of curvature R3form about 600 microns to about 750 microns, greater than radius ofcurvature R2. Diameter D3 is less than diameter D2. The convexly roundedtop surface is spaced apart from the glass article surface defining aheight H of the glass bump.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure will be better understood, and features, aspects andadvantages other than those set forth above will become apparent whenconsideration is given to the following detailed description thereof.Such detailed description makes reference to the following drawings,wherein:

FIG. 1 is a close-up cross-sectional view of a glass bump 60 formedaccording to an exemplary embodiment.

FIG. 2 is a schematic diagram of an example laser-based glass bumpforming apparatus used to form glass bumps 60 in a glass articleaccording to an exemplary embodiment.

FIG. 3 illustrates a graph of a photodetector electronic signal output(signal output (arbitrary units) vs. time (seconds)) during glass bumpgrowth according to an exemplary embodiment.

FIG. 4 is a plot diagram comparing height between a plurality oflaser-based glass bumps formed according to an exemplary embodiment ofthe present disclosure with height control versus height between aplurality of laser-based glass bumps formed according to theconventional methods without height control.

DETAILED DESCRIPTION

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which the disclosure belongs. Although any methods andmaterials similar to or equivalent to those described herein can be usedin the practice or testing of the present disclosure, the exemplarymethods and materials are described below.

A glass article of the present disclosure includes a surface and canhave any shape. In one example, the glass article can be round,spherical, curved, or flat. In another example the glass article can berelatively thick (about 10 cm) or relatively thin (about 0.1 mm). In yetanother example, the glass article has a thickness between about 0.5 mmand about 8 mm. In one embodiment, the glass article is comprised of aplurality of individual glass components (e.g., multiple square glassarticles which may be joined or fused together to a larger glassarticle). In an exemplary embodiment, the glass article is a glass pane20 made of a glass material and has top and bottom surfaces and an outeredge. Glass pane 20 of the present disclosure may be substantially flatacross its surfaces and may have a rectangular shape.

The glass article of the present disclosure may be formed from soda-limeglass, borosilicate glass, aluminosilicate glass, or an alkalialuminosilicate glass. Other suitable and available glasses andapplicable compositions are disclosed, for example, in U.S. PatentPublication No. 2012/0247063, the contents of which are incorporated byreference herein.

The glass article of the present disclosure comprises a plurality ofglass bumps 60. In one embodiment, the glass bumps are grown from thesurface of the glass article by a laser-irradiation process. Glass bumps60 of the present disclosure may be used as spacers between parallel,opposing panes of glass in a vacuum-insulated glass (VIG) window. In aVIG window, glass bumps 60 maintain the distance between the opposingglass panes that have a tendency to bow together under the force ofvacuum pressure there between and external atmospheric pressure andexternal forces (e.g., weather). Accordingly, the distance between theparallel, opposing panes of glass in VIG window is substantiallyequivalent to the heights of the glass bumps.

The present disclosure provides a glass article (e.g., glass pane 20)including a plurality of glass bumps having heights within a standarddeviation of each other. Minimal height variation between glass bumps 60used on VIG window pane reduce the stress concentration on individualbumps applied by the opposing glass pane in a VIG window. Conventionalglass bumps with a standard deviation of height greater than 1 microncauses stress (and potential defects) on the opposing glass pane wherethe taller glass bumps contact the opposing glass pane. Minimal heightvariation between glass bumps 60 used in a VIG window may also eliminatethe requirement for chemical-strengthening of the opposing glass pane towithstand the stress applied by glass bumps 60. In another example, theglass bumps 60 may act as spacers between the glass article and othermaterials (e.g., metal, plastic, etc.). In yet another example, theglass bumps 60 with minimal height variation may have aestheticadvantages.

Glass bumps 60 may be grown out of a body portion 23 of the glassarticle and formed from the glass material making up the glass article,so as to outwardly protrude in a convex manner from the glass articlesurface. In one embodiment, the glass article is comprised of aplurality of individual glass components, each glass component includingat least one locality L and/or at least one glass bump 60. The pluralityof glass bumps 60 may include any number of glass bumps including as fewas 20, 15, 10, 5 glass bumps, or less in the case of a statisticallysignificant number of glass bumps. The fewer number of bumps improvesthe optical quality of the glass article when used in a VIG window.However, in a VIG window, a sufficient number of bumps are required tosupport the weight of an opposing pane and other external forces. In anexample embodiment, glass bumps 60 are regularly spaced apart on theglass article with respect to each other. Distances between the glassbumps may be from about 1 mm (about 1/25 of an inch) to about 25centimeters (about 10 inches), or from about 1 centimeter (about 0.4inches) to about 15 centimeters (about 6 inches). Spacing the glassbumps closer together reduces stress concentration on individual bumpsin a VIG window. In another embodiment, the glass bumps are irregularlyor randomly spaced apart on the glass article with respect to eachother.

Referring to FIG. 1, an example of one of the plurality of glass bumpsis shown in a close-up cross-sectional view of a glass bump 60 on glasspane 20. Glass bump 60 is hemispherical shaped and includes a lowerregion 66 and an upper region 68 connected by an inflection region 67.Glass bump 60 has a height H60 measured from a surface 24 of glass pane20 to a terminal point 13. Terminal point 13 is the location on glassbump 60 at the furthest distance from the surface 24 of glass pane 20.In one embodiment, terminal point 13 may be an area on convexly roundedtop surface 52 of glass bump 60. Height H60 of glass bump 60 may rangefrom 50 microns to 200 microns, or from 75 microns to 150 microns, oreven from 100 microns to 120 microns in exemplary embodiments. Note thatif bump heights H60 are too small, the gap between opposing plates in aVIG window is reduced and, therefrom, a reduced vacuum space betweenopposing panes and reduced insulating properties. In addition, smallglass bump 60 heights H60 can lead to the appearance of optical ringsdue to light interference between closely arranged glass surfaces.

Lower region 66 of glass bump 60 projects from the surface of glass pane20 and is integrally formed thereon. Lower region 66 has a height H66that may extend from about 5% to about 25% of glass bump 60 height H60.Lower region 66 includes a volume V1 and a diameter D1 defined byconcavely rounded sides 53. Diameter D1 may be the maximum diameterD_(M) of glass bump 60. That is, maximum diameter D_(M) is the distancebetween the points A and B (shown in FIG. 1) where concavely roundedsides 53 terminate and join with surface 24 of glass pane 20. Maximumdiameter D_(M) may be from about 400 microns to about 800 micron, oreven 500 microns to 700 microns.

Concavely rounded sides 53 of lower region 66 include a radius ofcurvature R1. Concave radius of curvature R1 may be from about 25microns to about 100 microns. Radius of curvature R1 may vary slightlywithin the disclosed range at different locations around glass bump 60.Radius of curvature R1 is configured such that glass bump 60 projectsfrom glass pane 20 surface 24 so as not to exceed the disclosed rangefor diameter D1. Inflection region 67 of glass bump 60 connects lowerregion 66 and upper region 68. Upper region 68 includes a volume V2having a transition portion 69 and a top portion 70. Upper region 68 hasa height H68 that may extend from about 75% to about 95% of glass bump60 height H60. Transition portion 69 of upper region 68 includes adiameter D2 defined by convexly rounded sides 51. Diameter D2 may extendfrom about 33% to about 85% of maximum diameter D_(M) of glass bump 60.Convexly rounded sides 51 join with concavely rounded sides 53 extendingup from lower region 66 at inflection region 67. Convexly rounded sides51 have a convex radius of curvature R2. Convex radius of curvature R2may be from about 200 microns to about 400 microns and may vary slightlywithin the disclosed range at different locations around glass bump 60.

Radius of curvature R2 may be measured over at least 5 microns or 5% ofglass bump 60 height H60. Alternatively R2 may be measured over up to50% glass bump 60 height H60. Diameter D2, measured between convexlyrounded sides 51, may be from about 100 microns to about 600 microns.Diameter D2 of transition portion 69, from inflection region 67 to topportion 70, decreases by about 15% to about 65%. Diameter D2 is lessthan diameter D1 since the total diameter of glass bump 60 graduallydecreases from lower region 66 to transition portion 69.

Top portion 70 includes a diameter D3 defined by convexly rounded topsurface 52. Convexly rounded top surface 52 is spaced apart from glasspane 20 surface 24 defining height H60 of glass bump 60. Convexlyrounded top surface 52 may extend from about 1% to about 3% of glassbump 60 height H60. In other embodiments, convexly rounded top surface51 may extend from about 10% to about 30% of maximum diameter D_(M), orabout 20% to about 25% of maximum diameter D_(M). Convexly rounded topsurface 52 joins with convexly rounded sides 51 converging fromtransition portion 69. Convexly rounded top surface 52 has a convexradius of curvature R3 from about 600 microns to about 750 microns, orabout 650 microns to about 680 microns.

Radius of curvature R3 is configured to minimize contact betweenopposing glass panes in a VIG window and heat transfer between theopposing panes through glass bump 60. Radius of curvature R3 is suchthat it can be formed by a laser irradiation process of the presentdisclosure without the use of a growth-limiting structure. Thelaser-irradiation process of the present disclosure, free of agrowth-limiting structure, presents significant time savings for growingglass bumps 60 with a distinct radius of curvature on its convex topsurface as compared to conventional methods. Specifically, the need toalign the glass article relative to the growth-limiting structure beforegrowing glass bump 60 via laser-irradiation is eliminated.

In an exemplary embodiment, convex radius of curvature R3 is greaterthan the convex radius of curvature R2. In another embodiment, R3 isgreater than R2 by about 70% to about 140%, or about 75% to about 100%.In yet another embodiment, convex radius of curvature R3 is greater thanconcave radius of curvature R1. Diameter D3, measured as a chord onconvexly rounded top surface 51, is less than diameter D2. Diameter D3at its maximum may be from about 100 microns to about 264 microns.Diameter D3 decreases incrementally to a point at or around terminationpoint 13.

Transition portion 69 and top portion 70 are integrally formed together.Further, inflection region 67 connects the lower region 66 and upperregion 68 at transition portion 69. Inflection region 67 may be definedby sides without a radius of curvature (i.e., flat and perpendicular tosurface 24). In one embodiment, inflection region 67 is a 2-dimensionalarea (e.g., a plane). In another embodiment, inflection region 67 is avolume V4 extending at most about 5% of glass bump 60 height H60.

In the disclosed embodiment where glass bumps 60 have a hemisphericalshape, each glass bump may have a partial or complete circumference thatsubstantially corresponds to a general circle equation (e.g., x²+y²=r²)when overlaid thereon with a coefficient of determination from about 0.9to about 0.99. In another example embodiment where glass bumps 60 have ahemispherical shape, each glass bump has a lateral cross-section (asshown in FIG. 1) substantially matching a portion of a general circleequation with a coefficient of determination from about 0.9 to about0.99. In another embodiment, glass bumps 60 with a hemispherical shapedo not have a critical radius of curvature change point (seen for a“flat-top” glass bump or a glass bump with a top surface radius ofcurvature from about 900 microns to about 2600 microns) at theconnection between convexly rounded sides 51 and convexly rounded topsurface 52.

In one embodiment of the present disclosure, glass bumps 60 are formedby photo-induced absorption. Photo-induced absorption includes a localchange of the absorption spectrum of a glass article resulting fromlocally exposing (irradiating), or heating, the glass article withradiation (i.e., laser irradiation). Photo-induced absorption mayinvolve a change in adsorption at a wavelength or a range ofwavelengths, including but not limited to, ultra-violet, nearultra-violet, visible, near-infrared, and/or infrared wavelengths.Examples of photo-induced absorption in the glass article include, forexample, and without limitation, color-center formation, transient glassdefect formation, and permanent glass defect formation. Laserirradiation dose is a function of laser wavelength and a product oflaser power P and exposure time.

FIG. 2 is a schematic diagram of an example laser-based apparatus(“apparatus 100”) used to form glass bumps 60 in the glass article(e.g., glass pane 20). Apparatus 100 may include a laser 110 arrangedalong an optical axis A1. Laser 110 emits a laser beam 112 having powerP along the optical axis. In an example embodiment, laser 110 operatesin the ultraviolet (UV) region of the electromagnetic spectrum. Laserirradiation dose is a function of laser beam 112 wavelength and is aproduct of laser beam 112 power P and an exposure time.

Apparatus 100 also includes a focusing optical system 120 that isarranged along optical axis A1 and defines a focal plane P_(F) thatincludes a focal point FP. In an example embodiment, focusing opticalsystem 120 includes, along optical axis A1 in order from laser 110: acombination of a defocusing lens 124 and a first focusing lens 130(which combination forms a beam expander 131), and a second focusinglens 132. In an example embodiment, defocusing lens 124 has a focallength fD=−5 cm, first focusing lens 130 has a focal length fC1=20 cm,and second focusing lens 132 has a focal length fC2=2.5 cm and anumerical aperture NAC2=0.5. In another example embodiment, defocusinglens 124 and first and second focusing lenses 130 and 132 are made offused silica and include anti-reflection (AR) coatings. Alternateexample embodiments of focusing optical system 120 include mirrors orcombinations of mirrors and lens elements configured to produce focusedlaser beam 112F from laser beam 112.

Apparatus 100 also includes a controller 150, such as a lasercontroller, a microcontroller, computer, microcomputer or the like,electrically connected to laser 110 and adapted to control the operationof the laser. In an example embodiment, a shutter 160 is provided in thepath of laser beam 112 and is electrically connected to controller 150so that the laser beam can be selectively blocked to turn the laser beam“ON” and “OFF” using a shutter control signal SS rather than turninglaser 110 “ON” and “OFF” with a laser control signal SL.

Prior to initiating the operation of apparatus 100, the glass article isdisposed relative to the apparatus. Specifically, the glass article isdisposed along optical axis A1 so that a surface of the glass article issubstantially perpendicular to the optical axis A1. In an exampleembodiment, glass pane 20, including a front surface 22 and back surface24, is disposed relative to optical axis A1 so that back glass panesurface 24 is slightly axially displaced from focal plane P_(F) in thedirection towards laser 110 (i.e., in the +Z direction) by a distanceDF. In an example embodiment, glass pane 20 has a thickness TG in therange 0.5 mm≦TG≦6 mm. In another embodiment, 0.5 mm≦DF≦2 mm.

In an example method of operating apparatus 100, laser 110 may beactivated via control signal SL from controller 150 to generate laserbeam 112. If shutter 160 is used, then after laser 110 is activated, theshutter is activated and placed in the “ON” position via shutter controlsignal SS from controller 150 so that the shutter passes laser beam 112.Laser beam 112 is then received by focusing optical system 120, anddefocusing lens 124 therein causes the laser beam to diverge to form adefocused laser beam 112D. Defocused laser beam 112D is then received byfirst focusing lens 130, which is arranged to form an expandedcollimated laser beam 112C from the defocused laser beam. Collimatedlaser beam 112C is then received by second focusing lens 132, whichforms a focused laser beam 112F. Any point within the volume defined bythe intersections between the converging laser beam 112F and glass pane20 front surface 22 and back surface 24 is referred to herein as alocality L. Laser beam 112F may be focused on a different area of glasspane 20 to form another locality L.

Conventional methods of operating apparatus 100 include irradiating theglass article with a laser irradiation for a set period of time. Thatis, the glass article is exposed to laser beam 112F at a plurality oflocalities L on its surface with a fixed dose of laser irradiation.Thus, the laser is turned “ON” and “OFF” at the same interval at eachlocation to form glass bumps at each locality L. However, theseconventional methods do not consider, for example, variations or defectsin the glass article surface or structure, power output variations fromlaser 110, and/or other variables that may change between each pulse oflaser irradiation on the glass article surface. Accordingly,conventional laser irradiation methods result in a plurality of glassbumps with large height H variations and standard deviations. Specially,height H variation between the plurality of glass bumps formed byconventional laser irradiation methods may result in deviations greaterthan about 2 microns and/or standard deviation greater than or equal toabout 1.1 micron. Conventional methods of operating apparatus 100 alsoinclude using a growth-limiting structure (e.g., a plate) adjacent theglass article during glass bump formation to limit growth of the glassbump on the article to a certain height. As a result, glass bumps formedby conventional methods include a “flat-top” profile with an inflectionpoint between the convexly rounded side walls and the convexly roundedtop surface. This “flat-top” profile includes a convexly rounded topsurface (along 1-3% of height H) with a radius of curvature R5 fromabout 3000 microns to about 4500 microns.

In the present method of operating apparatus 100, laser beam 112Fcontacts glass pane 20 at a time increment Ti after laser 110 isactivated. Time increment Ti ends at or about when converging laser beam112F converges and contacts glass pane 20 front surface 22. Timeincrement Ti may vary from a picosecond to several seconds for eachlocality L as a result of, for example, laser 110 output variances,control signal SL or SS dead time, laser beam 112 travel time, shutter160 opening and closing time, and/or optical system 120 changes. Laserbeam 112 power P may be increased or decreased during time increment Ti.

As time increment Ti ends, time increment Tc begins as focused laserbeam 112F converges or when laser beam 112F contacts glass pane 20. Inan example embodiment, laser beam 112F contacts and passes through glasspane 20 and forms a focus spot S along optical axis A1 at focal pointFP. Focal point FP may be at distance DF from glass pane back surface 24and thus resides outside of body portion 23. It is noted here that glasspane 20 slightly affects the position of focal point FP of opticalsystem 20 because focused laser beam 112F converges as it passes throughthe glass pane. However, the thickness TG of glass pane 20 may besufficiently thin so that this focus-shifting effect can be ignored.

A portion of focused laser beam 112F is absorbed as it passes throughglass pane 20 (at locality L) due to the aforementioned photo-inducedabsorption in the glass pane. This serves to locally heat glass pane 20at locality L. The amount of photo-induced absorption may be relativelylow, e.g., about 3% to about 50%. When focused light beam 112F islocally absorbed in glass pane 20, a flash of light emanates fromlocality L.

The flash of light from locality L according to the present disclosureis a back flash of light from the front surface 22 of glass pane 20.That is, the flash of light emanates in a direction opposite thedirection of focused laser beam 112F (i.e., backwards). The back flashof light is not a detection of the focused laser beam though glass pane20 or on the back surface 24 of glass pane 20. Instead, the flash oflight is a detection of 20% to 100% of the maximum output signal 61 fromphotodetector 180, or even 35% to 85% of the maximum output signal 61from photodetector 180. The output signal 61 from photodetector 180 maycorrespond to fluorescence intensity emanating from locality L on thefront surface 22 of glass pane 20. Detecting the back flash of lightemanating from locality L on the front surface 22 of glass pane 20(i.e., where the laser beam 112F contacts glass pane 20) provides anadvantage over conventional methods in that bump heights are moreprecisely controlled (i.e., within a standard deviation of less than 1.1microns, or less). The change in fluorescence intensity emanating fromlocality L, detected as output signal 61, may be measured against themaximum output signal 61 from photodetector 180 or against contactoutput 15 registered by photodetector 180, corresponding to detectedlight emanating from locality L after laser beam 112F initially contactsglass pane 20. Without being limited to any particular theory, the flashof light emanating from laser irradiated locality L on the front surface22 of glass pane 20 may be molten glass at a temperature from about 900°C. to about 2000° C., or even about 900° C. to about 1500° C. In anexemplary embodiment, the flash of light is comprised of a broadspectrum of electromagnetic emission, including but not limited to,ultra-violet, near ultra-violet, visible, near-infrared, and/or infraredwavelengths.

Time increment Tc may conclude when the flash of light emanates fromlaser irradiated locality L. That is, time increment Tc continues fromwhen laser beam 112F contacts glass pane 20 until the flash of light isdetected by a photodetector 180. In this example, photodetector 180transmits an electronic signal 181 (e.g. as illustrated in the FIG. 3graph) to controller 150. In an exemplary embodiment, controller 150will recognize an output signal 61 within electronic signal 181 fromphotodetector 180. Thus, time increment Tc may continue from when laserbeam 112F contacts glass pane 20 until output signal 61 is received ordetected by controller 150 within electronic signal 181 fromphotodetector 180. Yet, in other embodiments, the flash of light may bedetected by any device (e.g., a photodiode) capable of detecting photonsof light, light energy, or luminescence and producing an electronicsignal 181 to controller 150. Following detection of the flash of light,controller 150 may be configured to adjust the laser beam 112 power P,set a time for continued operation of laser 110, or turn “OFF” laser 110(i.e., terminate laser irradiation) via control signal SL or SS.

The duration of time increment Tc may fluctuate between variouslocalities L in glass pane 20. This fluctuation or variance in theduration of time increment Tc between localities L may be from apicosecond to several milliseconds. Without being limited to anyparticular theory, this may be caused by fluctuations in laser 110output power P, glass article thickness, and/or compositional and/ormicrostructural differences at each locality L. Accordingly, eachlocality may require a slightly different laser irradiation dose toinitiate the flash of light.

The end of time increment Tc during laser irradiation begins an exposuretime Tf. In one embodiment, the start of exposure time Tf correspondswith the start of glass bump formation. The beginning of exposure timeTf may be adjusted by fractions of a second using various controlschemes. For example, controller 150 may be programmed to recognize the“ramping-up” (i.e., a large delta) output signal 61 within electronicsignal 181 from photodetector 180 to initiate time increment Tf. Thatis, controller 150 may be programmed to recognize from 20% to 100% ofthe maximum output signal 61 from photodetector 180, or even 35% to 85%of the maximum output signal 61 from photodetector 180. In anotherexample, controller 150 is programmed to initiate time increment Tf whenoutput signal 61 within electronic signal 181 reaches a chosen outputunit. In yet another example, controller 150 is programmed to recognizethe maximum or “peak” (i.e., 100% of photodetector 180 output signal 61)within electrical signal 181 from photodetector 180. In FIG. 3, the“peak” of output signal corresponds to 100% of the maximum output ofphotodetector 180. In yet another example, controller 150 may beprogrammed to recognize the “ramping-down” (i.e., a large delta) inoutput signal 61 within electronic signal 181 from photodetector 180 toinitiate time increment Tf. The laser irradiation dose at locality Lfollowing time increment Tc (i.e., during exposure time TO affectsheight H60 of the resultant glass bump 60.

At some time before or after the start of exposure time Tf the glassbump begins to form as a limited expansion zone is created within glasspane 20 body portion 23 in which a rapid temperature change induces anexpansion of the glass. Since the expansion zone is constrained byunheated (and therefore unexpanded) regions of glass surrounding theexpansion zone, the molten glass within the expansion zone is compelledto relieve internal stresses by expanding/flowing upward, therebyforming glass bump 60. If focused laser beam 112F has a circularlysymmetric cross-sectional intensity distribution, such as a Gaussiandistribution, then the local heating and the attendant glass expansionoccurs over a circular region in glass pane body 23, and the resultingglass bump 60 may be substantially circularly symmetric.

Generally, a longer duration of exposure time Tf at locality L resultsin an increased glass bump 60 height H60. Increased laser beam 112 powerP at locality L during exposure time Tf may also result in an increasedglass bump 60 height H60. Exposure time Tf and laser beam 112 power Pmay also have an effect on bump geometry. Controller 150 may beconfigured to adjust laser beam 112 power P during exposure time Tf.Exposure time Tf may be from a millisecond to several seconds dependingon the glass article composition and structure, and the desired bumpheight and geometry. In exemplary embodiments, exposure time Tf may befrom about a millisecond to about 5 seconds. In another exemplaryembodiment, laser power may be from a few watts to tens of watts, orabout 10 watts to about 20 watts.

In an exemplary method of operating apparatus 100, laser beam 112 powerP is held constant (e.g., at 15 watts) and exposure time Tf is a fixedtime from about 1 millisecond to about 2 seconds or more. In anotherembodiment of operating apparatus 100, laser beam 112 power P isincreased or decreased during fixed exposure time Tf. Contemplated UVwavelengths for effective glass bump 60 growth may be between about 340nanometers and about 380 nanometers. Contemplated IR wavelengths foreffective glass bump 60 growth may be between 750 nanometers and 1600nanometers. Other wavelengths on the electromagnetic spectrum are alsocontemplated, for example, between 300 nanometers and 1600 nanometers.After exposure time Tf, laser 110 may be turned “OFF” with a lasercontrol signal SL or shutter control signal SS such that glass pane 20is not contacted by laser beam 112F. Thus, exposure time Tf ends whenlocality L is no longer contacted by laser beam 112F. The resultingglass bump 60 grown from locality L is fixed by terminating laser beam112F irradiation at locality L. Thereafter, glass bump 60 may be fixedby rapid radiative cooling.

Referring to FIG. 3, an example electronic signal output graph fromphotodetector 180 in arbitrary units versus time (e.g., seconds) showingelectronic signal 181 during glass bump 60 growth. In exemplaryembodiments, electronic signal 181 corresponds to the signal produced byphotodetector 180 and sent to controller 150. In FIG. 3, time incrementTi is shown between (1) laser 110 activation and (2) converging laserbeam 112F contacting glass pane 20. After laser beam 112F contacts glasspane 20, photodetector 180 registers a contact output 15 correspondingto detected light emanating from locality L. In example embodiments,light detected at contact output 15 is less than 20% of the maximumoutput signal 61 from photodetector 180. Time increment Tc is shownbetween (2) converging laser beam 112F contacting glass pane 20 and (3)the start of the flash of light. During time increment Tc, photodetector180 registers a relatively constant output of light detection. Timeincrement Tf is shown between (3) the start of the flash of light and(4) termination of glass pane 20 exposure to laser beam 112F. The flashof light is indicated as a distinct, sharp output signal 61 (i.e., from20% to 100% of the maximum output signal 61) from photodetector 180during time increment Tf. In an exemplary embodiment, controller 150 isconfigured not to mischaracterize contact output 15 as output signal 61(i.e., the flash of light).

The aforementioned process can be repeated at different locations (e.g.,localities L) in the glass pane to form a plurality (e.g., an array) ofglass bumps 60 in glass pane 20. In an example embodiment, apparatus 100includes an X-Y-Z stage 170 electrically connected to controller 150 andconfigured to move glass pane 20 relative to focused laser beam 112F inthe X, Y and Z directions, as indicated by large arrows 172. This allowsfor a plurality of glass bumps 60 to be formed by selectivelytranslating stage 170 via a stage control signal ST from controller 150and irradiating different locations in glass pane 20. In another exampleembodiment, focusing optical system 120 is adapted for scanning so thatfocused laser beam 112F can be selectively directed to locations inglass pane 20 where glass bumps 60 are to be formed.

As mentioned above, conventional methods of operating apparatus 100include irradiating the glass article with a laser irradiation for a setperiod of time (e.g., Ti+Tc+Tf=1.8 seconds). That is, the glass articleis exposed to laser beam 112F at a plurality of localities L with afixed dose of laser irradiation.

By controlling the laser irradiation dose at each locality L only duringexposure time Tf according to the present methods, each glass bump 60has a more controlled height H60 as compared to glass bumps formed byconventional methods. Specifically, the present methods of operatingapparatus 100 result in a plurality of glass bumps 60 with a standarddeviation of less than 1.1 microns, or less than 1 micron, or even lessthan 0.5 micron. In alternative embodiments, the standard deviation maybe 0 microns, or greater than 0.1 micron. Accordingly, controlling thelaser irradiation dose at each locality L during exposure time Tf (afterthe flash of light is detected) allows more precise control of height Hof glass bumps 60 during laser irradiation formation.

Glass articles having a plurality of glass bumps with heights within astandard deviation of 1 micron can be used in windows. For example,glass bumps of the present disclosure may be used as spacers betweenparallel, opposing panes of glass in a vacuum-insulated glass (VIG)window. The distance between the parallel, opposing panes of glass inVIG window is substantially equivalent to the heights of the glassbumps. An advantage of minimal height variance (less than 1 micron, or0.5 micron, and greater than 0.1 micron) is the minimization ofmechanical stresses at the contact point between glass bump 60 terminalpoint 13 and the opposing glass pane. In another example, the bumps mayacts as spacers between the glass article and other materials. In yetanother example, the glass bumps with minimal height variation may haveaesthetic advantages.

EXAMPLES

The methods of the present disclosure for controlling height amongst aplurality of glass bumps grown on a glass article with laser irradiationwill be further clarified with reference to the following examples.

Example 1

In this example a soda-lime glass pane (4 mm thickness) was disposedrelative to a laser apparatus similar to apparatus 100 described above.The apparatus and laser were operated consistent with conventionalmethods (i.e., without the use of a photodiode to detect a flash oflight from a laser irradiated locality). That is, the height controlmethods of the present disclosure where not used. 18 glass bumps wereformed by laser irradiation at a distance apart from each other on theglass pane.

During laser exposure at each locality L, the laser was set at 15 wattswith a UV wavelength of 355 nanometers. The total time for exposure ofthe glass pane's 18 localities to laser irradiation was set as fixed at1.8 seconds (i.e., Ti+Tc+Tf=1.8 seconds). That is, each of the 18localities individually received the same dose of laser radiation(ignoring potential laser output variations) to form each of the 18glass bumps.

Following the laser irradiation operation, the glass bumps heights Hwere measured, using an optical scanning profilometer, from the glasspane surface to the highest terminal point. FIG. 4 illustrates theheight measurements of each of the 18 resultant glass bumps for thisexample with square data points 200. Table 1 below provides a numericalsummary of the FIG. 4 results. The average height for the 18 glass bumpsof this example was 185.4 μm. The maximum deviation and minimumdeviation from the average height was 2.1 and −2.4, respectively.Accordingly, the standard deviation for the glass bumps heights of thisexample was 1.1 microns.

Example 2

In this example, the soda lime glass pane from Example 1 was disposedrelative to the same laser apparatus as described in Example 1. In thisexample however, a photodiode was disposed adjacent to the glass panenear the surface first exposed to the laser. That is, as illustrated inFIG. 2, the photodiode 180 was arranged above the front surface 22 ofthe glass pane 20 in close proximity to locality L. The apparatus andlaser were operated consistent with the presently disclosed methods forcontrolling the height of glass bumps to form 18 glass bumps at adistance apart from each other on the glass pane.

During operation of the laser at each locality L, the laser was set at15 watts with a UV wavelength of 355 nanometers. In this example, timeincrements Ti and Tc were not set, fixed increments for each of the 18localities. Instead, after the flash of light was detected (i.e., outputsignal 61 ramping up) by controller 150, only exposure time Tf was fixedat 1.6 seconds. The inventors chose 1.6 seconds for exposure time Tfbecause time increments Ti and Tc were estimated at 0.2 seconds duringExample 1. Accordingly, laser irradiation was initiated at each localityindividually. After the photodiode detected the flash of light from alocality, the controller terminated laser irradiation at that locality1.6 seconds thereafter. Time increments Ti and Tc were not controlled ormeasured in any way. Again, the photodiode electronic signal 181 fromone of these localities is illustrated in FIG. 3.

Following the laser irradiation operation, the glass bumps 60 heights Hwere measured from the glass pane surface to the highest terminal point.Also, the radius of curvature R3 of the convexly rounded top surface(along the top 1-3% of height H60) of plurality of glass bumps wasmeasured as between about 600 microns to about 750 microns. FIG. 4illustrates the narrow height distribution measurements for each of the18 resultant glass bumps for this example with diamond data points 201.Table 1 below provides a numerical summary of the FIG. 4 results. Theaverage height for the 18 glass bumps of this example was 188.9 microns.Unexpectedly, the maximum deviation and minimum deviation from theaverage height was 1.3 and −0.7, respectively. Further unexpected, thestandard deviation for the glass bumps heights of this example was 0.5microns.

TABLE 1 Comparison of Example 1 and Example 2 Bump Height Measurementsshown in FIG. 4. Example 1 Bump Heights shown as Example 2 Bump Heightsshown as square data points 200 diamond data points 201 (without heightcontrol) (with height control) Number of bumps 18 Number of bumps 18Average bump 185.4 microns Average bump 188.9 microns height height Maxdeviation 2.1 microns Max deviation 1.3 microns Min deviation −2.4microns Min deviation −0.7 microns Standard deviation 1.1 micronsStandard deviation 0.5 microns

It was unexpected that the glass bumps in Example 2 had a more than 50%standard deviation of height reduction as compared to Example 1 glassbumps. By reducing control of the laser radiation dose at each localityuntil the flash of light is detected by the photodiode, the heightdistribution is reduced for glass bumps formed according to the presentmethods. One of ordinary skill would have expected to see an increasedstandard deviation of glass bump height by reducing control of laserirradiation dose at a particular locality. That is, by only controllingexposure time Tf (and not controlling time increments Ti and Tc), one ofordinary skill in the art would have expected to increase the standarddeviation of height for the glass bumps above 1.1 microns. Instead, thestandard deviation of height for the 18 glass bumps in Example 2 wasreduced to below 1 micron, in fact, 0.5 micron.

The difference in average bump height between Example 1 and Example 2can be attributed to an increased laser irradiation dose for Example 2glass bumps as compared to Example 1 glass bumps. Specifically, Example2 bumps were likely irradiated for a longer period of time based on the0.2 second time estimation for time increments Ti and Tc from Example 1.The average bump height of Example 2 glass bumps could be adjusted bysimply reducing exposure time Tf from 1.6 seconds to 1.5 seconds or lessfor example.

As used herein, the singular forms “a,” “an,” and “the” include pluralreferents unless the context clearly dictates otherwise. Thus, forexample, reference to a “metal” includes examples having two or moresuch “metals” unless the context clearly indicates otherwise.

Ranges can be expressed herein as from “about” one particular value,and/or to “about” another particular value. When such a range isexpressed, examples include from the one particular value and/or to theother particular value. Similarly, when values are expressed asapproximations, by use of the antecedent “about,” it will be understoodthat the particular value forms another aspect. It will be furtherunderstood that the endpoints of each of the ranges are significant bothin relation to the other endpoint, and independently of the otherendpoint.

Unless otherwise expressly stated, it is in no way intended that anymethod set forth herein be construed as requiring that its steps beperformed in a specific order. Accordingly, where a method claim doesnot actually recite an order to be followed by its steps or it is nototherwise specifically stated in the claims or descriptions that thesteps are to be limited to a specific order, it is no way intended thatany particular order be inferred.

It is also noted that recitations herein refer to a component of thepresent invention being “configured” or “adapted to” function in aparticular way. In this respect, such a component is “configured” or“adapted to” embody a particular property, or function in a particularmanner, where such recitations are structural recitations as opposed torecitations of intended use. More specifically, the references herein tothe manner in which a component is “configured” or “adapted to” denotesan existing physical condition of the component and, as such, is to betaken as a definite recitation of the structural characteristics of thecomponent.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the present inventionwithout departing from the spirit and scope of the invention. Sincemodifications combinations, sub-combinations and variations of thedisclosed embodiments incorporating the spirit and substance of theinvention may occur to persons skilled in the art, the invention shouldbe construed to include everything within the scope of the appendedclaims and their equivalents.

What is claimed is:
 1. A method of forming a glass article comprising aplurality of glass bumps, the glass article having a surface, the glassbumps formed in the glass article by laser radiation, each glass bumphaving a terminal point at a distance from the glass article surface,wherein a standard deviation of the distance between the glass articlesurface and the terminal points of the plurality of glass bumps is lessthan 1 micron, the method comprising: irradiating the glass article withlaser radiation at a plurality of localities to induce growth of theglass bumps at the plurality of localities on the glass article;detecting a back flash of light from the laser irradiated localities onthe glass article with a photodetector that generates an electronicsignal; setting a fixed exposure time for the laser radiation at theplurality of localities for after the back flash of light is detected;and controlling a laser irradiation dose at the plurality of localitiesand the distance between each glass bump terminal point and the glassarticle surface, using the electronic signal, by terminating laserradiation of the localities the fixed exposure time after a controllerreceives the electronic signal.
 2. The method of claim 1 wherein theplurality of glass bumps includes at least 10 glass bumps.
 3. The methodof claim 1 wherein each of the plurality glass bumps include ahemispherical lateral cross-section, wherein each lateral cross-sectionsubstantially corresponds to a general circle curve equation with acoefficient of determination from 0.9 to 0.99.
 4. The method of claim 1wherein the standard deviation of the distance between the glass articlesurface and the terminal points of the plurality of glass bumps is lessthan 0.5 micron.
 5. The method of claim 1 wherein the glass article isirradiated with laser radiation with a UV wavelength between 340nanometers and 380 nanometers to induce growth of the glass bumps. 6.The method of claim 1 wherein detecting the back flash of light from thelaser irradiated localities includes sensing molten glass at atemperature from 900° C. to 2000° C.
 7. The method of claim 1 whereindetecting the back flash of light from the laser irradiated localitiesoccurs at a time increment after laser radiation starts.
 8. The methodof claim 1 wherein controlling the laser irradiation dose includes acontroller configured to adjust the laser radiation power after thecontroller receives the electronic signal.
 9. A method of forming aglass pane comprising a plurality of hemispherical glass bumps, theglass pane having a surface, the glass bumps grown on the glass panesurface by laser irradiation, each glass bump having a height spacedapart from the glass pane surface, wherein a standard deviation ofheight between the plurality of glass bumps is less than 1 micron, themethod comprising: irradiating the glass pane with laser radiation toinduce growth of one of the glass bumps at one of a plurality oflocalities on the glass pane; detecting, at a time increment afterirradiating one locality with the laser irradiation, a back flash oflight from that laser irradiated locality with a photodetector; settinga fixed exposure time for the laser radiation of each locality for afterthe back flash of light is detected; and terminating a laser radiationdose at the locality at the fixed exposure time after the photo detectordetects the back flash of light.
 10. The method of claim 9 wherein eachof the hemispherical glass bumps include a lateral cross-section,wherein the lateral cross-section of each of the plurality ofhemispherical glass bumps substantially matches a general circle curveequation with a coefficient of determination from 0.9 to 0.99.
 11. Themethod of claim 9 wherein the glass pane is used in a vacuum insulatedwindow, the plurality of hemispherical glass bumps on the glass panespace the glass pane from another glass pane at a distance substantiallyequivalent to the height of the hemispherical glass bumps.
 12. Themethod of claim 9 wherein detecting the back flash of light from thelaser irradiated locality includes identifying molten glass at the laserirradiated locality at a temperature from 900° C. to 2000° C.
 13. Themethod of claim 9 further comprising controlling the laser radiationdose at the locality by adjusting the laser radiation power after thephoto detector detects the back flash of light.
 14. The method of claim9 further comprising controlling the laser radiation dose at thelocality by adjusting the fixed exposure time for laser radiation afterthe photo detector detects the back flash of light.
 15. The method ofclaim 9 wherein the fixed exposure time is from 1 millisecond to 5seconds.
 16. The method of claim 9 wherein the glass pane is comprisedof a plurality of glass components, the glass components each include atleast one of the localities.
 17. The method of claim 9 wherein the glasspane is comprised of a plurality of glass components, each glasscomponent including at least one hemispherical glass bump formedtherein.